Method for efficiently transmitting physical channel in multi-carrier aggregation state to support broadband

ABSTRACT

The present invention relates to a wireless connection system, and more specifically to a method for efficiently transmitting a control channel in a multi-carrier aggregation state. According to one aspect of the invention, a method for enabling a terminal to transmit data in a broadband wireless connection system that supports multiband comprises the steps of: receiving uplink acknowledgement information from a base station through a first downlink component carrier among plural downlink component carriers available in the terminal; transmitting data to the base station through an uplink resource indicated by the uplink acknowledge information; and receiving feedback information from the base station through the first control channel of the first downlink component carrier, wherein the feedback information indicates whether there is an error in the reception of the transmitted data.

TECHNICAL FIELD

The present invention relates to a wireless access system, and moreparticularly to a method for effectively transmitting a control channelin a multi-carrier aggregation state.

BACKGROUND ART

A brief description of carriers will be given hereinbelow.

The amplitude, frequency, and/or phase of a sine wave or a periodicpulse wave may be modulated to include information. The sine wave orpulse wave serving to convey information is called a carrier.

Methods for modulating a carrier include single-carrier modulation (SCM)and multi-carrier modulation (MCM). In SCM, modulation is performed suchthat all information is carried on a single carrier.

MCM divides an entire channel bandwidth of one carrier into subchannelshaving multiple narrow bandwidths and transmits multiple narrowbandsubcarriers through respective subchannels.

When using MCM, each subchannel may approximate to a flat channel due toa narrow bandwidth. A user may compensate for channel distortion using asimple equalizer. MCM may be implemented at a high speed using FastFourier Transform (FFT). Namely, MCM is favored over SCM duringhigh-rate data transmission.

As the capabilities of abase station and/or a terminal have beendeveloped, a frequency bandwidth which can be provided or used by thebase station and/or the terminal has been increased. Accordingly, in theembodiments of the present invention, a multi-carrier system supportinga broadband service by aggregating one or more carriers is proposed.

Specifically, the multi-carrier system, which will be describedhereafter, uses carriers by aggregating one or more carriers, unlike theafore-mentioned MCM scheme which uses carriers by segregating onecarrier.

To efficiently use multiple bands or multiple carriers, a technique inwhich one medium access control (MAC) entity manages multiple carriers(e.g., multiple frequency carriers) has been proposed.

FIGS. 1( a) and 1(b) illustrate methods for transmitting and receivingsignals based on a multi-band radio frequency (RF) scheme.

In FIGS. 1( a) and 1(b), one MAC layer in each of a transmitting end anda receiving end may manage multiple carriers to efficiently use themultiple carriers. To effectively transmit and receive the multiplecarriers, it is assumed that both the transmitting end and the receivingend can transmit and receive multiple carriers. Since frequency carriersmanaged by one MAC layer do not need to be contiguous, the above methodenables flexible resource management. More specifically, the frequencycarriers may have contiguous aggregation or non-contiguous aggregation.

In FIGS. 1( a) and 1(b), physical layers (PHY 0, PRY 1, . . . , PHY n-2,and PHY n-1) represent multiple bands and each of the bands may have afrequency carrier (FC) size allocated for a specific service accordingto a predetermined frequency policy. For example, PHY 0 (RF carrier 0)may have a frequency band size allocated for a general FM radiobroadcast and PHY 1 (RF carrier 1) may have a frequency band sizeallocated for cellular phone communication.

Although each frequency band may have a different FA size depending onthe characteristics thereof, it is assumed in the following descriptionthat each frequency carrier (FC) has a size of A MHz for convenience ofexplanation. Each frequency allocation (FA) band may be represented by acarrier frequency that enables a baseband signal to be used in eachfrequency band. Thus, in the following description, each FA will bereferred to as a “carrier frequency band” or will simply be referred toas a “carrier” representing each carrier frequency band unless such usecauses confusion. As in the recent 3rd generation partnership project(3GPP) long term evolution-advanced (LTE-A), the carrier may also bereferred to as a “component carrier” to discriminate it from asubcarrier used in the multi-carrier system.

As such, the “multi-band” scheme may also be referred to as a“multi-carrier” scheme or a “carrier aggregation” scheme.

In order to transmit a signal through multiple bands as shown in FIG. 1(a) as well as to receive a signal through multiple bands as shown inFIG. 1( b), it is necessary for a transceiver to include a RadioFrequency (RF) module that transmits and receives signals throughmultiple bands. In FIG. 1, a method for constructing the Medium AccessControl (MAC) layer “MAC” is decided by a base station (BS) irrespectiveof downlink (DL) and uplink (UL).

In brief, FIG. 1 shows signal transmission/reception technology forenabling one MAC entity (simply referred to as a MAC) to manage/operatea plurality of RF carriers. In addition, RF carriers managed by one MACneed not be contiguous to one another. Therefore, the above-mentionedsignal transmission/reception technology of the present invention ismore flexible in terms of resource management. However, according touser requirements or channel environment, a MAC entity for each carriercan manage/operate individual carriers as shown in FIG. 1.

FIG. 2 exemplarily shows a frequency allocation method for use in acarrier aggregation system.

In FIG. 2, frequency carrier (FC 0 to FC 7) may be managed by RFs (RF 0to RF 7). In FIG. 2, it is assumed that FC 0, FC 2, FC 3, FC 6 and FC 7have already been allocated to a specific conventional communicationservice. In the meantime, available RFs (RF 1(FC 1), RF 4(FC 4), and RF5(FC 5)) can be effectively managed by one MAC (MAC #5). In this case,RF carriers constructing one MAC may not be contiguous to one another asdescribed above, such that it is possible to more effectively managefrequency resources.

However, a multiband-based communication scheme for use with a currentmobile communication technology has been conceptually defined. Ifnecessary, the multiband-based communication scheme may only requirefurther assignment of a Frequency Carrier (FC). Therefore, a method fortransmitting and receiving signals to implement more efficient andhigher-performance processing, and methods for transmitting andreceiving a physical channel need to be more specifically defined.

DISCLOSURE Technical Problem

The present invention is directed to a method for effectivelytransmitting a physical channel in a multi-carrier aggregation situationsupporting a broadband that substantially obviates one or more problemsdue to limitations and disadvantages of the related art.

An object of the present invention is to provide an effectivecommunication system and method.

Another object of the present invention is to provide a method foreffectively transmitting and receiving a physical channel in amultiband-based communication environment.

A further object of the present invention is to provide a method fordeciding a downlink component carrier via which a Physical Hybrid ARQIndicator Channel (PHICH) is efficiently transmitted in amultiband-based communication environment.

It will be appreciated by persons skilled in the art that the objectsthat can be achieved by the present invention are not limited to whathas been particularly described hereinabove and the above and otherobjects that the present invention can achieve will be more clearlyunderstood from the following detailed description taken in conjunctionwith the accompanying drawings.

Technical Solution

To achieve these objects and other advantages and in accordance with thepurpose of the invention, as embodied and broadly described herein, thepresent invention provides a method for efficientlytransmitting/receiving a physical channel and a method fortransmitting/receiving data in a wireless communication system employingmultiple carriers (multi-carrier).

In another aspect of the present invention, a method for transmittingdata by a user equipment (UE) in a broadband wireless access systemsupporting multiple bands includes receiving uplink (UL) grantinformation from a base station (BS) through a first downlink (DL)component carrier from among several DL component carriers available inthe user equipment (UE), transmitting data to the base station (BS)through uplink (UL) resources indicated by the UL grant information, andreceiving feedback information indicating whether a reception error ofthe transmitted data occurs through a first control channel of the firstDL component carrier.

The uplink (UL) resources may be uplink resources of an upl ink (UL)component carrier not linked to the first DL component carrier.

The reception of the feedback information may be performed irrespectiveof a ratio between the number of DL component carriers available in theuser equipment (UE) and the number of UL component carriers available inthe user equipment (UE).

The first control channel may be a Physical Hybrid ARQ Indicator Channel(PHICH).

In another aspect of the present invention, a method for enabling a basestation (BS) to receive data from a user equipment (UE) in a broadbandwireless access system supporting multiple bands includes transmittinguplink (UL) grant information to a user equipment (UE) through a firstdownlink (DL) component carrier from among several DL component carriersavailable in the user equipment (UE), receiving data from the userequipment (UE) through uplink (UL) resources indicated by the UL grantinformation, determining whether a reception error occurs in thereceived data, and transmitting feedback information depending on thedetermined result to the user equipment (UE) through a first controlchannel of the first DL component carrier.

The feedback information may be transmitted through the first DLcomponent carrier only.

The uplink (UL) resources may be uplink resources of an uplink (UL)component carrier not linked to the first DL component carrier.

The transmission of the feedback information maybe performedirrespective of a ratio between the number of DL component carriersavailable in the user equipment (UE) and the number of UL componentcarriers available in the user equipment (UE).

The first control channel may be a Physical Hybrid ARQ Indicator Channel(PHICH).

In yet another aspect of the present invention, a user equipment (UE)operated in a broadband wireless access system supporting multiple bandsincludes a processor, and a radio frequency (RF) module for receiving aradio frequency (RF) signal from an external part upon receiving acontrol signal from the processor, demodulating/decoding the received RFsignal, transmitting the decoded result to the processor,modulating/encoding data received from the processor, and transmittingthe encoded result to an external part. Upon receiving uplink (UL) grantinformation from a base station (BS) through a first downlink (DL)component carrier from among available DL component carriers, theprocessor transmits data to the base station (BS) through uplink (UL)resources indicated by the UL grant information, receives feedbackinformation indicating whether a reception error occurs in thetransmitted data from the base station (BS) through a first controlchannel of the first DL component carrier, and exchanges data with thebase station (BS).

The uplink (UL) resources may be uplink resources of an uplink (UL)component carrier not linked to the first DL component carrier.

The processor maybe configured to receive the feedback informationthrough the first control channel of the first DL component carrier,irrespective of a ratio between the number of DL component carriersavailable in the user equipment (UE) and the number of UL componentcarriers available in the user equipment (UE).

The first control channel may be a Physical Hybrid ARQ Indicator Channel(PHICH).

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

ADVANTAGEOUS EFFECTS

the exemplary embodiments of the present invention have the followingeffects.

First, the embodiments of the present invention can provide effectivecommunication.

Second, the embodiments of the present invention can enable physicalchannels of a Long Term Evolution (LTE) system to be transmitted andreceived in a multi-carrier environment.

Third, when using a method for deciding a physical hybrid ARQ indicatorchannel (PHICH) according to the present invention, a user equipment(UE) (or a mobile station (MS)) need not monitor control regions of alldownlink component carriers, resulting in a reduction in blind decodingoverhead of the UE.

It will be appreciated by persons skilled in the art that that theeffects that can be achieved with the present invention are not limitedto what has been particularly described hereinabove and other advantagesof the present invention will be more clearly understood from thefollowing detailed description taken in conjunction with theaccompanying drawings.

DESCRIPTION OF DRAWINGS

FIGS. 1( a) and 1(b) illustrate methods for transmitting and receivingsignals based on a multi-band radio frequency (RF) scheme.

FIG. 2 exemplarily shows a method for allocating a frequency in amulti-carrier system.

FIGS. 3( a) and 3(b) exemplarily show a method for enabling a pluralityof medium access control (MAC) layers to manage a plurality of carriers.

FIGS. 4( a) and 4(b) exemplarily show a method for enabling one MAClayer to manage one or more carriers.

FIGS. 5 and 6 show methods for establishing a carrier bandwidth in amulti-carrier system.

FIG. 7 shows another method for establishing a carrier bandwidth in amulti-carrier system.

FIG. 8 shows physical channels for use in a 3GPP LTE system serving asone example of a mobile communication system and a general signaltransmission method using the physical channels.

FIGS. 9( a) and 9(b) show examples of an asymmetric carrier aggregationapplicable to embodiments of the present invention.

FIG. 10 shows a transmission format of a physical hybrid ARQ indicatorchannel (PHICH) under a cross-carrier scheduling situation according toanother embodiment of the present invention.

FIG. 11 is a block diagram illustrating a transmitter and a receiveraccording to another embodiment of the present invention.

MODE FOR INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. The detailed description, which will be given below withreference to the accompanying drawings, is intended to explain exemplaryembodiments of the present invention, rather than to show the onlyembodiments that can be implemented according to the present invention.The following detailed description includes specific details in order toprovide a thorough understanding of the present invention. However, itwill be apparent to those skilled in the art that the present inventionmay be practiced without such specific details. For example, thefollowing description will be given centering upon a 3rd GenerationPartnership Project Long Term Evolution (3GPP LTE) mobile communicationsystem, but the present invention is not limited thereto and theremaining parts of the present invention other than uniquecharacteristics of the 3GPP LTE system are applicable to other mobilecommunication systems.

In some cases, in order to prevent ambiguity of the concepts of thepresent invention, conventional devices or apparatuses well known tothose skilled in the art will be omitted and denoted in the form of ablock diagram on the basis of the important functions of the presentinvention. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

In the fol lowing description, “terminal” may refer to a mobile or fixeduser equipment (UE), for example, a user equipment (UE), a mobilestation (MS) and the like. Also, “base station” (BS) may refer to anarbitrary node of a network end which communicates with the aboveterminal, and may include a Node B (Node-B), an eNode B (eNB) and thelike.

In the embodiments of the present invention, a medium access control(MAC) layer may be used as a generic name of an upper layer conceptuallyhigher than a physical layer PHY (or layer 1) according to the OpenSystems Interconnection (OSI) 7 layer. In addition, although frequencycarriers are configured to be contiguous to each other in the drawings,it should be noted that the frequency carriers may not be physicallycontiguous to each other.

A wireless environment considered in the present invention includes allgeneral multi-carrier supporting environments. In other words, amulti-carrier system (also called a carrier aggregation system) for usein the embodiments of the present invention is configured to aggregateone or more carriers, each of which has a bandwidth smaller than that ofan objective bandwidth, so as to construct and support a broadbandservice. When at least one carrier having a bandwidth that is less thanthat of the objective band, a bandwidth of the aggregated carrier may belimited to a bandwidth used in a conventional system so as to satisfydownward compatibility with a conventional IMT system. For example, theconventional 3GPP LTE system supports bandwidths of 1.4 MHz, 3 MHz, 5MHz, 10 MHz, 15 MHz, and 20 MHz. The LTE_A system is configured tosupport a bandwidth larger than 20 MHz by aggregating theabove-mentioned bandwidths supported by the LTE system. Alternatively, anew bandwidth may be defined irrespective of a bandwidth used in theconventional system, such that a carrier aggregation can be supported bythe new bandwidth.

In addition, the term ‘carrier aggregation’ used in the presentinvention may include a contiguous carrier aggregation in whichcontiguous carriers can be aggregated, and a non-contiguous carrieraggregation (or a spectrum aggregation) in which non-contiguousaggregations can be aggregated. In addition, the carrier aggregation maybe conceptually mixed with bandwidth (BW) aggregation as necessary.

FIGS. 3( a) and 3(b) exemplarily show a method for enabling a pluralityof MAC layers to manage a plurality of carriers.

FIG. 3( a) shows a one-to-one mapping relationship between MAC layersand physical layers when a transmitter (Base Station BS) supportsmultiple carriers. FIG. 3( b) shows a one-to-one mapping relationshipbetween MAC layers and physical (PHY) layers when a receiver (UE)supports multiple carriers. In this case, one physical layer may use onecarrier.

FIGS. 4( a) and 4(b) exemplarily show a method for enabling one MAClayer to manage one or more carriers. In FIGS. 4( a) and 4(b), MAClayers managing specific carriers (Carrier 0 and Carrier 1) may beindependently mapped to respective physical layers, or one MAC layermanaging one or more specific carriers (Carrier n-2 and Carrier n-1) maybe mapped to respective physical layers.

FIG. 4( a) shows a one-to-one or one-to-m (where m<1) mappingrelationship between MAC layers and physical layers when a transmittingend (base station) supports multiple carriers. FIG. 4( b) shows aone-to-one or one-to-m mapping relationship between MAC layers andphysical layers when a receiving end (UE) supports multiple carriers.

In a system supporting multiple carriers, carriers used by each terminalmay differ according to capabilities of the base station (BS) and theUE. However, carrier band support abilities of the base station (BS) maybe uniformly determined. The base station (BS) and the UE may negotiatewith each other to decide whether to support carriers during call setupaccording to the capabilities of the base station (BS).

In the embodiments of the present invention, information as to carriersupport of the UE, that is, information as to whether an arbitraryterminal can support an RF of a specific range or a specific frequencycarrier may be one reference for identifying terminal (UE) categories.

Therefore, the base station (BS) and/or UE specify a specific range or aspecific carrier according to UE categories or UE classes. Hence, thebase station (BS) and the UE can negotiate with each other according toUE classes as to whether to support multiple carriers, whether tosupport simultaneous reception processing, simultaneous receptionprocessing or adaptive carrier selection, parallel or sequentialprocessing classification, and values such as carrier support range.

As an implicit UE category specification method, UE categories can beimplicitly identified based on a one-to-one mapping relationship byother parameters such as a reception available band of a UE or peak datarate thereof.

The base station (BS) may specify supportable frequency carrier RFs incell-specific radio resource control (RRC) information to transmit thespecified RFs to any base station (BS) or UEs within a cell. Forexample, the base station (BS) may transmit supportable frequencycarrier RFs to any base station (BS) or UEs within a cell through aprimary broadcast channel (P-BCH), cell-specific RRC signaling, abroadcast control channel (BCCH), a dedicated broadcast channel (DBCH),or SU information.

Conversely, a UE may include information as to frequency carrier RFs,which can be received when accessing any base station (BS) or a cell, ina profile or may inform a base station (BS) of the information throughadditional signaling.

A base station (BS) including a downlink scheduler and/or an uplinkscheduler may semi-statically update information as to frequency carrierRFs which can be allocated to individual terminals. Accordingly, thebase station (BS) can transmit the information as to frequency carrierRFs to individual terminals through UE-specific RRC signaling (or higherlayer signaling).

For example, the base station (BS) may semi-statically transmitinformation as to candidate bands, which can be used by each terminal,i.e., information as to which carrier can be used by the UE, to UEsthrough RRC signaling.

In a multi-carrier system supporting transmission and reception ofmultiple carriers, a central frequency and a carrier bandwidth may bedifferently set according to each carrier. In addition, the number offrequency carriers, which can be supported by each base station (BS) andeach UE to transmit and receive carriers, a detailed central frequency,and a frequency bandwidth may be differently set according to UEcategories (e.g., UE levels) or base station (BS) categories (e.g., basestation levels, cell levels, cluster levels, or network levels).

In a circumstance in which the base station (BS) applies multiplecarriers, content of necessary setup information and various controlinformation according to setup, and a transmitting/receiving methodtherefor may be differently applied according to setting levels of UEcategories or base station (BS) categories.

To set a central frequency of an international mobiletelecommunications-advanced (IMT-A) or LTE-A system, the following twomethods may be considered.

1. Method for locating a central frequency on multiple carriers whilemaintaining a frequency raster of an IMT system (or LTE system); and

2. Method for independently locating a central frequency regardless of afrequency raster of an IMT system.

Moreover, to support a wider system bandwidth of the IMT-A system than asystem bandwidth of the IMT system, two methods for setting a bandwidthof each carrier included in multiple frequency carriers may beconsidered. For example, a method of operating multiple carriersdepending on a target system bandwidth may be considered. Namely, amethod for differently constructing the number of carriers or abandwidth of each carrier may be considered to support a target systembandwidth.

FIGS. 5 and 6 illustrate methods for setting a bandwidth of a carrier ina multi-carrier system.

A method for allocating a bandwidth of a carrier is as follows.

To support a target system bandwidth, a user symmetrically allocates abasic frequency block in both directions on the basis of a specificcentral frequency. Thereafter, a frequency carrier (FC) less than thebasic frequency block may be allocated to the other bands less than AMHz. At this time, even when allocating the frequency carrier to thebands less than A MHz, a necessary frequency carrier is symmetricallyallocated in both directions to allocate the target system bandwidth.

In FIG. 5, a system bandwidth is set to 100 MHz and a central frequencyis set to 50 MHz. In FIG. 10, a system bandwidth is set to 70 MHz and acentral frequency is set to 35 MHz. Various bandwidths ranging from 20MHz to 100 MHz may be supported by a terminal (e.g., UE).

FIG. 6 illustrates another method for setting a bandwidth of a carrierin a multi-carrier system.

To support a target system bandwidth, a user allocates a bandwidth inunits of a basic frequency block. Thereafter, a frequency carrier lessthan the basic frequency block may be asymmetrically allocated to theother bands less than A MHz.

Referring to FIG. 7, a basic frequency is first allocated in an overallsystem bandwidth and then a central frequency is set. In this case, afrequency bandwidth may be asymmetrically allocated based on the centralfrequency.

In the LTE system, each UE is unable to recognize which one of physicalresources is used to transmit a control channel of the UE istransmitted. In addition, each UE is unable to recognize which subframewill receive a control channel of the UE. Therefore, each UE can receiveits own control channel using a blind decoding method in which each UEdecodes all control channels until receiving the UE control channel.

In a mobile communication system, the user equipment (UE) may receiveinformation from the base station (BS) via downlink, and the UE maytransmit information via uplink. A variety of data and controlinformation may be transmitted from and received in the UE, and avariety of physical channels may be used according to categories andusages of transmission- or reception-information of the UE.

FIG. 8 is a conceptual diagram illustrating physical channels for use ina 3GPP system and a general method for transmitting a signal using thephysical channels.

Referring to FIG. 8, when powered on or when entering a new cell, a UEperforms initial cell search in step S801. The initial cell searchinvolves synchronization with a BS. Specifically, the UE synchronizeswith the BS and acquires a cell Identifier (ID) and other information byreceiving a Primary Synchronization CHannel (P-SCH) and a SecondarySynchronization CHannel (S-SCH) from the BS. Then the UE may acquireinformat ion broadcast in the cell by receiving a Physical BroadcastCHannel (PBCH) from the BS. During the initial cell search, the UE maymonitor a downlink channel status by receiving a downlink ReferenceSignal (DL RS).

After the initial cell search, the UE may acquire more specific systeminformation by receiving a Physical Downlink Control CHannel (PDCCH) andreceiving a Physical Downlink Shared CHannel (PDSCH) based oninformation of the PDCCH in step S802.

On the other hand, if the UE initially accesses the BS or if the UE doesnot have radio resources for signal transmission, it may perform arandom access procedure to the BS in steps S803 to S806. For the randomaccess, the UE may transmit a specific sequence as a preamble to the BSon a Physical Random Access CHannel (PRACH) in step S803 and receive aresponse message for the random access on a PDCCH and a PDSCHcorresponding to the PDCCH in step S804. In the case of contention-basedRACH other than the handover case, the UE may perform a content ionresolution procedure by transmitting an additional PRACH in step S805and receiving a PDCCH and a PDSCH in step S806.

After the foregoing procedure, the UE may receive a PDCCH and a PDSCH instep S807 and transmit a Physical Uplink Shared CHannel (PUSCH) and aPhysical Uplink Control CHannel (PUCCH) in step S808, as a generaldownlink/uplink (DL/UL) signal transmission procedure. Here, uplinkcontrol information transmitted from the UE to the BS or downlinkcontrol information transmitted from the UE to the BS may include adownlink (DL) or uplink (UL) ACKnowledgement/Negative ACKnowledgment(ACK/NACK) signal, a Channel Quality Indicator (CQI), a Precoding MatrixIndex (PMI) and/or a Rank Indicator (RI). The UE adapted to operate inthe 3GPP LTE system may transmit the control information such as a CQI,a PMI, and/or an RI on the PUSCH and/or the PUCCH.

The initial cell search procedure shown in FIG. 8 needs to be changed ina multi-carrier environment of the present invention. The initial cellsearch procedure for use in the multi-carrier environment according tothe present invention will hereinafter be described in detail.

In the initial cell search procedure, the UE may attempt to detect asynchronous channel (SCH) signal in units of a frequency raster.

If the synchronous channel (SCH) signal has been successfully detectedin one of the aggregated downlink carriers, the detected carrier may beset to a downlink (DL) reference carrier or a primary carrier. In thiscase, the UE may receive a physical cell ID. Even when the correspondingcarrier is not set to the reference carrier, the downlink carrier fromwhich the SCH signal has been detected will hereinafter be referred toas a reference carrier for convenience of description and betterunderstanding of the present invention.

The UE may receive a primary broadcast channel (P-BCH) from a referencecarrier, such that it can receive a downlink transmission bandwidth, aPhysical Hybrid ARQ Indicator Channel (PHICH), a system frame number(SFN), the number of Tx antennas of the BS, etc.

In order to acquire information required for initial access, the UEreceives system information (SI-x) transmitted as a reference carrier.The system information (SI-x) includes an uplink (UL) bandwidth,uplinkE-UTRA Absolute Radio Frequency Channel Number (UL EARFCN), higherlayer signaling related to setting of several UL/DL channels. That is,if the UE recognizes an absolute radio frequency channel number (EARFCN)of a UL carrier and a bandwidth thereof by receiving system information,the UE can acquire information regarding a DL-UL pair band for use infrequency division multiplexing (FDM).

The UE may set the UL carrier, that has acquired information, to a ULreference carrier. As described above, in the case where a referencecarrier is not established separately in uplink, a UL carrier linked toa DL carrier in which a synchronous channel (SCH) signal has beendetected is referred to as a reference carrier for convenience ofdescription and better understanding of the present invention.

The BS transmits cell-specific multi-carrier setup information through aDL reference carrier, and enables the UE to recognize a carrier setup ofthe corresponding cell. In this case, the same physical cell ID may betransmitted through synchronous channel signals of multiple DL carriersaggregated in one cell, and different physical cell IDs maybetransmitted according to individual carriers. If the UE has alreadyrecognized carrier setup information of the cell, it is able to change acarrier through a simple handover procedure.

The cell-specific multi-carrier setup information may be transmittedthrough extended system information (extended SI-x) for a UE dependingon the LTE-A standard, or maybe transmitted to a UE through a reservedpart from among a primary broadcast channel (P-BCH) defined in a generalLTE standard (LTE Rel. 8). As another transmission method, cell-specificmulti-carrier setup information may be contained in broadcast- orsystem-information of the corresponding cell, or may also be containedin an EARFCN of the corresponding cell.

The cell-specific multi-carrier setup information may includeinformation indicating a DL carrier from among multiple carriers of thecorresponding cell, information of a carrier frequency, DL/UL carrierlinkage information of the corresponding cell, and the like.

If multiple DL carriers contained in the same cell have the samephysical cell IDs, DL carrier information within the cell, which hasbeen acquired from the cell-specific multi-carrier setup information,can be used, such that the UE may not receive a P-BCH, systeminformation (SI-x), and a synchronous channel.

Conversely, if multiple DL carriers within the cell have differentphysical cell IDs, a UE detects a synchronous channel in each DL carrierusing DL carrier information acquired from the cell-specificmulti-carrier setup information, such that it receives a physical cellID of each carrier. The UE may generate a reference signal sequence foreach carrier and perform scrambling and the like using the receivedphysical cell ID. Thereafter, the UE may receive a P-BCH and systeminformation, and recognize information of a UL carrier linked to each DLcarrier.

If link information of DL/UL carriers within the cell is transmittedseparately, the UE may recognize link information irrespective of thepresence or absence of system information.

The Present Invention—Linkage

A detailed description of a carrier aggregation method based on alinkage between DL and UL carriers capable of being assigned to anarbitrary UE in a multi-carrier system will be given below.

Carrier aggregation methods may be divided into two methods, i.e., acell-specific method and a UE-specific method. The term “cell-specific”may indicate a carrier setup from the viewpoint of an arbitrary cell ora BS. If the term “cell” indicates one downward compatible carrier orone downward incompatible carrier, the term “cell-specific” may be usedfor carriers (managed by an arbitrary BS), each of which is representedby a cell.

1) Cell-Specific Aggregation (Cell-Specific DL/UL Linkage)

Cell-specific carrier aggregation may be established by either anarbitrary BS or cell. Cell-specific carrier aggregation for use infrequency division multiplexing (FDM) may be configured to decide alinkage of DL and UL according to a default Tx-Rx separation defined inthe LTE Rel-8 and/or LTE-A standard.

2) UE-Specific Carrier Aggregation (UE-Specific DL/UL Linkage)

The UE-specific carrier aggregation may be configured in the form of acarrier aggregation capable of being used by a specific UE or UE groupusing a predetermined method (UE capability, negotiation, signaling,broadcasting, etc.) used between a BS and a UE. For example, theUE-specific carrier aggregation defined in the LTE-A is as follows.

UE downlink (DL) component carrier (CC) set: UL DL component carrier setis a set of DL component carriers, that can be established throughdedicated signaling and be scheduled in such a manner that the UE canreceive a PDSCH via downlink.

UE UL component carrier (CC) set: UE UL component carrier set is a setof UL component carriers, that can be scheduled in such a manner thatthe UE transmits a PUSCH via uplink.

In addition to the above-mentioned two CC sets, the present inventioncan further define the following CC sets.

Physical downlink control channel (PDCCH) monitoring set: Differentlyfrom a UE DL/UL component carrier set, the PDCCH monitoring set may becontained in a UE DL component carrier set, be configured to includesome parts of the UL component carrier set, or be subject to the UE DLcomponent carrier set or other component carriers. The UE monitors aphysical downlink control channel (PDCCH) contained in the PDCCHmonitoring set. The PDCCH monitoring set may have cell-specificcharacteristics.

Measurement set: As a carrier aggregation technique is recentlyintroduced, the amount of measurement results to be reported from the UEto the BS is naturally increased. In order to reduce the amount ofreporting overhead or in order to effectively measure UE capability, ameasurement set may be defined.

The above-mentioned methods for constructing the aforementionedUE-specific carrier aggregation may be classified according toflexibility. For example, a UE-specific carrier aggregation (DL/ULlinkage) may be established irrespective of a cell-specific carrieraggregation, and may also be established within the scope in which theUE-specific carrier aggregation does not escape from the cell-specificcarrier aggregation structure.

Next, methods for constructing a carrier aggregation according to thepresent invention can be classified according to a linkage formatdependent upon the number of UL component carriers or DL componentcarriers assigned to one UE (irrespective of UE-specific orcell-specific status).

1) Symmetry

In a symmetrical format, a DL component carrier and a UL componentcarrier are linked to each other one by one, such that the ratio of thenumber of DL component carriers to the number of UL component carriersis set to 1:1.

2) Asymmetry

In an asymmetrical format, the number of DL component carriers isdifferent from the number of UL component carriers. In other words, theUL component carrier and the DL component carriers are not linked toeach other one by one, and a detai led description thereof willhereinafter be described with reference to FIG. 9.

FIGS. 9( a) and 9(b) show examples of an asymmetric carrier aggregationapplicable to embodiments of the present invention.

FIG. 9( a) shows one example in which the number of DL componentcarriers is higher than the number of UL component carriers. In FIG. 9(a), one UL component carrier is linked to two DL component carriers(DL:UL=2:1). For convenience of description and better understanding ofthe present invention, the example of FIG. 9( a) is referred to as a ‘DLheavy’.

Next , FIG. 9( b) shows one example in which the number of UL componentcarriers is higher than the number of DL component carriers. In FIG. 9(b) , two UL component carriers are linked to one DL component carrier(DL:UL=1:2). For convenience of description and better understanding ofthe present invention, the example of FIG. 9( b) is referred to as ‘ULheavy’.

Methods for constructing a carrier aggregation can be classifiedaccording to a carrier scheduling format in a carrier aggregationenvironment.

1) General Scheduling

In a multi-carrier environment according to the present invention, aphysical downlink control channel (PDCCH) of an arbitrary DL componentcarrier may include resource allocation information of a physicaldownlink shared channel (PDSCH) having the same DL component carrier asin the PDCCH and resource al locat ion information of a physical uplinkshared channel (PUSCH) of one UL component carrier linked to thecorresponding DL component carrier.

In other words, general scheduling may indicate an exemplary case inwhich resource allocation information of other DL component carriersand/or UL component carriers is not contained in a downl ink controlchannel of an arbitrary DL component carrier while the BS performsscheduling. In this case, a downlink control channel information (DCI)format of the general LTE Rel-8 and a physical downlink control channel(PDCCH) transmission structure may be used without change. Therefore,transmission of an associated physical downlink shared channel (PDSCH),transmission of UL control information (e.g., UL HARQACK/NACK), andtransmission of an uplink shared channel may satisfy various mattersdefined in the general LTE standard.

2) Cross Carrier Scheduling

Differently from general scheduling, a physical downlink shared channel(PDSCH) having anther downlink component carrier (DL CC) maybe scheduledthrough a physical downlink control channel (PDCCH) of an arbitrary DLcomponent carrier. Alternatively, a physical uplink shared channel(PUSCH) that is transmitted according to a UL grant transmitted throughan arbitrary DL component carrier, may be transmitted through another ULcomponent carrier different from a UL carrier linked to a DL componentcarrier having received the UL grant. The above-mentioned case willhereinafter be referred to as ‘cross carrier scheduling’ in the presentinvention.

The cross carrier scheduling requires carrier indication information toindicate which UL component carrier and/or which UL component carrierare adapted to transmit a PDSCH and/or PUSCH indicated by a PDCCH. Suchcarrier indication information is contained in a DL grant or UL grant,and is then transmitted to the UE. In addition, according to the crosscarrier scheduling, transmission of a PDSCH, transmission of a ULACK/BACK, transmission of a PUSCH, and transmission of a PHICH need tobe changed.

In addition, information as to whether cross carrier scheduling isallowed may be ‘UE-specific’, ‘UE group-specific’, or ‘cell-specific’.Carrier indication information (i.e., CI bits field) dependent upon theallowance of cross carrier scheduling may be activated/deactivated byexecuting semi-static signaling at an arbitrary OSI layer.

The present invention provides a variety of methods for effectivelytransmitting/receiving physical channels according to theabove-mentioned individual carrier aggregation formats (e.g., DL/ULasymmetry, DL/UL symmetry, and/or cross carrier scheduling).

Physical Control Channel Format Indicator Channel (PCFICH)

First, a method for effectively transmitting/receiving a PCFICH in amulti-carrier environment according to one embodiment of the presentinvention will hereinafter be described in detail.

The embodiment of the present invent ion provides the following threemethods to transmit the PCFICH, and a detailed description thereof willbe described in detail.

Method 1

PCFICH may be carrier-specifically transmitted through all DL componentcarriers. The first method (Method 1) may effectively manage and useresources of a control information region of each carrier. For theseoperations, respective DL carriers may be transmitted with differentcontrol channel format indicators (CFIs). If necessary, the PCFICH maynot be transmitted according to carrier characteristics, and this meansthat an LTE-format PDCCH is not contained in a carrier. In this case, ifa control channel is contained in a specific carrier, a general LTEterminal (legacy UE) may not access the corresponding carrier, andseparate accessible control channel information may be assigned to theLTE-A terminal.

Method 2

PCFICH contains common carrier information such that a control channelformat indicator (CFI) may be commonly transmitted. In this case, acommon carrier PCFICH may be transmitted through all aggregated DLcomponent carriers, or may also be transmitted through one or morespecific carriers only.

Method 3

PCFICH may have common carrier information in units of a group, suchthat it can be carrier-commonly transmitted in units of a group in whicha control channel format indicator (CFI) is decided. In this case, agroup-based common carrier PCFICH may be transmitted through allaggregated DL component carriers within the corresponding group, or mayalso be transmitted through one or more specific carriers only.

The first to third methods (Methods 1 to 3) will hereinafter bedescribed in detail.

If PDCCHs via which respective DL component carriers are transmitteddiffer in size, especially, if PDCCH need not be transmitted to allaggregated DL component carriers, it is preferable that a controlchannel format indicator (CFI) value be carrier-specifically transmittedas shown in the first method (Method 1).

In order to prevent a PDCCH from being allocated in a correspondingcarrier (i.e., in order to support zero PDCCH allocation), four states(or four indexes) formed by a control channel format indicator (CFI)having the size of 2 bits may be used. That is, the number of OFDMsymbols used for transmission of a physical downlink control channel(PDCCH) is sequentially set to 1, 2, 3, and 0, and 0, 1, 2, and 3(0b00˜ob11) are sequentially mapped to 1, 2, 3, and 0 OFDM symbols insuch a manner that the size of the PDCCH can be indicated. 2 bits of thecontrol channel format indicator (CFI) according to the general LTEstandard are obtained by correcting the result mapped in the order of{1, 2, 3, reserved}, and a general mapping result of 2 bits can bemaintained within a narrow system bandwidth (BW). In order to preventincorrect interpretation of such a control channel format indicator(CFI), CFI correction dependent upon the first method (Method 1) may beexcluded in a specific situation (e.g., a DL component carrier and anarrow bandwidth setup are simultaneously implemented while a downlinkcarrier is established).

In a DL carrier aggregation situation, zero PHICH allocation, in which aPhysical Hybrid ARQ Indicator Channel (PHICH) is not allocated to a DLcomponent carrier to which no PHICH is assigned, may be indicated. Inthis case, a 1 bit field indicating allocation or non-allocation of aPHICH is assigned to a primary BCH (P-BCH), or a specified systeminformation class (SI-x class) of the LTE system is established as cellcommon system information on a broadcast control channel (BCCH) and thusthe SI-x class is transmitted. Although such system information (SI-xclass) may be transmitted in the same carrier, it actually affects thestandard that enables a PHICH structure to obtain system information(SI-x class), such that information regarding corresponding controlchannels may be contained in a specific carrier related to a carrierincluding no PHICH. In association with the above-mentioned description,if no PHICH is assigned, a zero PDCCH status may always be indicatedthrough a control channel format indicator (CFI) of a PCFICH on theassumption that no PDCCH is transmitted in a corresponding DL carrier.However, in the case where some specific and/or UE-specific PDCCHsaretransmitted on a DL carrier indicating non-allocation of a PHICH, acontrol channel format indicator (CFI) indicating the number of OFDMsymbols allocated to a PDCCH may be transmitted through a PCFICH.However, the use of a special value may cause ambiguity of a PDCCHstructure, such that it is preferable that an operation for accessing aspecific carrier be limited for each UE. In this case, a control channelformat indicator (CFI) on a DL carrier in which PHICH transmission isconducted is set to a specific value indicating non-allocation of aPDCCH, so that the set value may be transmitted to the UE through aPCFICH.

A method for effectively transmitting a PCFICH when cross carrierscheduling is allowed according to one embodiment of the presentinvention will hereinafter be described in detail.

A PDCCH and a PDSCH for an arbitrary UEA may be transmitted throughdifferent carriers. For example, it is assumed that an arbitrary BSsupports three DL component carriers (DL CCs #1, #2, #3) and three ULcomponent carriers (UL CCs #1, #2, #3) for the UE A. In this case, aPDCCH of the UE A may be transmitted to a DL CC #1, and a PDSCHindicated by a corresponding PDCCH may be transmitted to a DL CC #2 or#3.

In more detail, it is assumed that a PDSCH is transmitted through a DLCC #2, and the UE A decodes a control channel format indicator (CFI)(that is transmitted over a PCFICH) of the DL CC #1 without generatingany errors, so that no problems occur in a Cyclic Redundancy Check (CRC)check of a PDCCH. In this case, the UE A must also decode a PCFICH ofthe DL CC #2 without generating any errors so as to decode a PDSCH ofthe DL CC #2 indicated by a PDCCH of the DL CC #1.

In the case where a PDCCH and a PDSCH are transmitted through the samecarrier as in the general LTE Rel-8 system, a PCFICH decoding error ofthe corresponding carrier inevitably causes a PDCCH decoding error. Inaddition, if the PDCCH decoding error has occurred, the UE does notdecode a PDSCH. In this case, the UE decides that there is no scheduleddata in the UE, and does not decode a PDSCH, so that the UE does notperform any operation in a feedback (HARQ) response subframe for thecorresponding data. The BS transmits a PDCCH to an arbitrary UE at then-th subframe, expects to receive a feedback (HARQ) response to a PDSCHindicated by the corresponding PDCCH at the (n+4)-th subframe. However,if the BS does not receive a feedback (HARQ) response, retransmission ofthe corresponding data is not performed, and new transmission isperformed.

However, if cross carrier scheduling is allowed in the same manner as inthe LTE-A, unexpected problems may occur. For example, although a PDCCHhas been successfully decoded (i .e. PDCCH CRC OK) by correctly decodinga PCFICH of a first DL component carrier to which a PDCCH istransmitted, there may occur a failure in PCFICH decoding of a second DLcomponent carrier to which a PDSCH is transmitted. In this case, the UEinevitably fails to receive a PDSCH of the second DL component carriersuch that a NACK response to the corresponding PDSCH is transmitted tothe BS. Since the UE transmits a NACK response to the correspondingPDSCH, the BS transmits a retransmission packet to the UE. However,herein, the UE wrongly decodes a PCFICH, and stores incorrect PDSCH datacaused by the PCFICH decoding error in a buffer so that unexpectedproblems are continuously encountered in a PDSCH HARQ process. In moredetail, the UE does not store information regarding a packet causing aPDSCH decoding error in the buffer under the condition that a PCFICH iscorrectly decoded, such that it stores incorrect PDSCH data caused bythe PCFICH decoding error in the buffer, resulting in the occurrence ofproblems in a PDSCH HARQ process.

One embodiment of the present invention provides the following methodsso as to minimize not only the number of PCFICH decoding errorsencountered in the aforementioned cross carrier scheduling but also thenumber of HARQ process problems caused by such PCFICH decoding error.

1) Firstly, One embodiment of the present invention provides a methodfor simultaneously transmitting not only a carrier indicator fieldserving as carrier indication information indicating which DL componentcarrier is used to transmit a PDSCH, but also a control channel formatindicator value of the corresponding DL component carrier. That is, aPDCCH may include a control channel format indicator value of a DLcomponent carrier at which a PDSCH indicated by the corresponding PDCCHis to be received.

In this case, afield for a control channel format indicator valuecontained in a PDCCH DCI format may be contained in the PDCCH only whencross carrier scheduling is enabled. If cross carrier scheduling isactivated (enabled), the UE can recognize a control channel formatindicator value of a DL component carrier at which a PDSCH is to bereceived, using the control channel format indicator (CFI) value thathas been received through a PDCCH. Alternatively, under the conditionsdescribed above, the UE may recognize i) a control channel formatindicator value of a DL component carrier (at which a PDSCH is to bereceived) through a control channel format indicator value contained inthe PDCCH, or may also recognize ii) the same control channel formatindicator value of the DL component carrier by decoding a PCFICH of a DLcomponent carrier at which a PDSCH is to be received. Under the sameconditions, according to still another method, the UE may recognize i) acontrol channel format indicator value of a DL component carrier (atwhich a PDSCH is to be received) through a control channel formatindicator contained in the PDCCH, and may also recognize ii) the samecontrol channel format indicator value of the DL component carrier bydecoding a PCFICH of a DL component carrier at which a PDSCH is to bereceived, in such a manner that information as to whether or not thecontrol channel format indicator value is duplicated can be recognized.

If the UE repeatedly confirms the control channel format indicator asdescribed above, UE operations can be classified according to thefollowing two cases.

First, according to one case of the two cases, a control channel formatindicator value of a PDCCH is identical to a control channel formatindicator value contained in a PCFICH of a DL component carrier to whicha PDSCH is to be transmitted. In this case, the UE decides that acontrol channel format indicator value of a DL component carrier atwhich a PDSCH is to be received has been correctly decoded, receives aPDSCH according to scheduling allocation information indicated by thePDCCH, and performs a feedback procedure (i.e., HARQ procedure)according to the PDSCH reception result.

Conversely, a detailed description of the other case in which a controlchannel format indicator value of aPDCCH is different from a controlchannel format indicator value of a PCFICH of a DL component carrier atwhich the PDSCH is to be received will hereinafter be described indetail. In this case, the UE decides that the control channel formatindicator value of a DL component carrier at which a PDSCH is to bereceived has been wrongly decoded. That is, the UE decides that a PDCCHhas been correctly decoded by CRC-processing a PDCCH, but decides that acontrol channel format indicator value of a DL component carrier atwhich a PDSCH is to be received has been wrongly decoded. In this case,the UE does not decode a PDSCH using the correctly decoded PDCCHinformation (that is, PDSCH scheduling information received at a PDCCH,a carrier indicator for a DL component carrier to which thecorresponding PDSCH is to be transmitted, and information regarding acontrol channel format indicator). Instead of using the correctlydecoded PDCCH information, it is preferable that the UE transmits noHARQ response information to the BS in the same manner as in a UEfailing to receive a PDCCH. That is, it is assumed that, although the BSfor use in the general LTE Rel-8 transmits a PDCCH to the UE, the UEfails to correctly decode the corresponding PDCCH, so that the UE mayperform the procedure specified to solve the above-mentioned problem. Incontrast, the UE may decode a PDSCH on the basis of PDCCH information.That is, in order to decode a PDSCH using the scheduled carrier, aPCFICH value needs to be decoded. Herein, if this PCFICH value isdifferent from a value indicated by a PDCCH, the UE may have priorityover the PCFICH value at a PDCCH completely verified by a CRC. In thiscase, in order to decode a PDSCH, the UE may acquire information to beused for selecting a data symbol from PDCCH information for which CRCverification has been completed.

2) Secondly, from the viewpoint of a scheduler, the same control channelformat indicator value may be assigned to individual component carriers(CCs) (i.e., component carriers to which a PDCCH and a PDSCH indicatedby the corresponding PDCCH are transmitted) serving as a target of thecross carrier scheduling.

3) Thirdly, control channel format indicator values of all DL componentcarriers serving as a target of cross carrier scheduling managed by anarbitrary BS are established to be identical in terms of time. That is,in the case where one carrier in which cross carrier scheduling is notallowed and the other case in which cross carrier scheduling is allowedare simultaneously present in a plurality of carriers managed by one BS,the same control channel format indicator value is assigned to eachcarrier for which cross carrier scheduling is allowed. In addition, anindependent control channel indicator value may be assigned to othercarriers for which cross carrier scheduling is not allowed. In otherwords, control channel format indicator values of all DL componentcarriers serving as a target of the cross carrier scheduling areidentical to one another, but a control channel format indicator valueper subframe may be variably established.

If the UE has successfully decoded a PDCCH of an arbitrary DL componentcarrier under the cross carrier scheduling situation, this means that acontrol channel format indicator value of the corresponding DL componentcarrier has been correctly decoded through a PCFICH. Therefore, the UEcan receive a PDSCH of a DL component carrier indicated by a carrierindicator field using the control channel format indicator value of theDL component carrier that has received the PDCCH. In this case, the UEmay receive i) a PDSCH without decoding a PCFICH of a different DLcomponent carrier to which a PDSCH is to be transmitted using a PCFICHvalue of a DL component carrier that has received a PDCCH, and maydetermine ii) whether a control channel format indicator is duplicatedby decoding a PCFICH of a DL component carrier to which a PDSCH is to betransmitted, and then decode the PDSCH.

4) Fourthly, control channel format indicator values of variouscomponent carriers (CCs) related to one BC component carrier (i.e., a BCcomponent carrier to which a PDCCH is transmitted, a different BCcomponent carrier to which a PDSCH indicated by the BC component carrieris transmitted, an NBC component carrier, and an extended componentcarrier) maybe established to be identical to a control channel formatindicator value of a component carrier to which a PDCCH is transmitted.

In this case, an NBC component carrier and/or an extended componentcarrier, each of which transmits a PDSCH, may be limited to componentcarriers linked to a UL component carrier linked to the BC componentcarrier to which a PDCCH is transmitted, or may be establishedirrespective of linkage to the UL component carrier.

5) Fifthly, through a component carrier (UE-specific primary componentcarrier or a cell-specific primary component carrier) capable of beingdecoded by each LTE-A UE supporting the cross carrier scheduling orthrough system information of a component carrier to which a PDCCH is tobe transmitted, control channel format indicators of other componentcarriers may be transmitted to each UE.

6) Sixthly, If one carrier includes an independently operating frequencydomain and an extended segment defined as an extended frequency domainof the frequency domain, the PCFICH value may be differently analyzed orinterpreted. In other words, a PCFICH value of the independentlyoperating part is applied only to a corresponding frequency domain, thesame or different value as the PCFICH value may be selectively appliedto the extended region of the frequency domain. That is, if the samevalue as the PCFICH value is assigned to and used in the frequencydomain and the extended frequency domain, a PDSCH part of the extendedfrequency domain is started in the same manner as in the independentfrequency domain. On the other hand, if a control channel as in the LTEsystem is not established in the extended frequency domain according tothe LTE-A system characteristics, the PDSCH may have the same startposition as in a subframe or may start from the position of the OFDMsymbol having a constant offset. In this case, the offset value may besignaled.

Physical Downlink Control Channel (PDCCH)

A method for effectively transmitting and receiving a PDCCH in amulti-carrier environment according to another embodiment of the presentinvention will hereinafter be described in detail.

Although the embodiment of the present invention assumes a DL heavystatus in which two DL carriers are linked to one UL carrier as shown inFIG. 9( a), it should be noted that the embodiment of the presentinvention can also be applied to multi-carrier aggregation of thesymmetrical- and UL heavy-types without departing from the scope andspirit of the present invention.

The UL grant serving as control information including schedulinginformation of a physical uplink shared channel (PUSCH) of an arbitraryUL component carrier may be transmitted through two DL componentcarriers linked to the UL component carrier. In this manner, if the ULgrant information is transmitted through all DL carriers linked to oneUL component carrier, efficiency of resources used for transmission of adownlink control channel may be deteriorated. In addition, since a UE isunable to recognize which downlink carrier is to be used fortransmission of the UL grant, the UE has to perform blind decoding ofall DL component carriers linked to the corresponding UL componentcarrier.

Therefore, this embodiment of the present invention provides a methodfor transmitting UL grant information through one DL component carrierinstead of all DL component carriers linked to one UL component carrier.As a result, resources used for transmission of a DL control channel canbe efficiently used, resulting in a reduction in complexity of the blinddecoding of the UE.

A variety of methods for selecting a downlink component carrier to whichUL grant information is transmitted according to another embodiment ofthe present invention will hereinafter be described in detail.

1) First Method: If a primary carrier is decided and selected from amonga plurality of DL component carriers linked to one UL carrier accordingto a predetermined method, the UL grant information may be transmittedthrough the corresponding DL primary carrier. In this case, the primarycarrier may be cell-specific, UE-specific, or UE group-specific. In thiscase, the primary carrier may be established per DL/UL linkageregardless of downlink (DL) and uplink (UL).

2) Second Method: When determining the order of DL component carrierslinked to one UL carrier, the UL grant may be transmitted through thefirst or last carrier on the basis of a DL EARFCN.

3) Third Method: In association with DL component carriers linked to oneUL component carrier, a DL component carrier to which one UL grant is tobe transmitted may be determined using a predefined rule such as ahashing function known to the BS. In this case, the DL component carriermay be cell-specific, UE-specific, or UE group-specific.

4) Fourth method: If the number of DL carriers capable of being accessedby the LTE-based UE from among a plurality of DL component carriers islimited to a predetermined number (less than the total number of DLcomponent carriers), the UL grant may be any one of DL componentcarriers capable of being accessed by the LTE-based UE, such that acommon design (i.e., downward compatibility) related to the LTE standardcan be guaranteed. In contrast, in order to implement load balancing, ULgrant information for the LTE-A UE may be transmitted through a DLcomponent carrier that can be accessed by the LTE-A UE only.

5) Fifth Method: Assuming that a specific DL component carrier can beaccessed by the LTE-based UE according to the above-mentioned fourthmethod, this means that the corresponding carrier satisfies a defaultFDD Tx-Rx separation specified in the LTE Rel-8. Therefore, providedthat the ratio of DL carriers to UL carriers is set to 2:1, only oneDL/UL pair can satisfy the above-mentioned default FDD Tx-Rx separation.For the above-mentioned reason, only one of two DL component carrierscan be accessed by the LTE-based UE, and the UL grant can be transmittedonly through such a DL component carrier.

6) Sixth Method: Under the same conditions as in the fifth method, thesixth method may restrict and enable a PDCCH (i.e., UL grantinformation) supporting cross scheduling to be transmitted at a DLcomponent carrier that satisfies the Rel-8 default Tx-Rx separationcondition.

7) Seventh Method: The seventh method can determine a DL componentcarrier, that can automatically transmit UL grant information by a UE IDassigned to each UE, from among DL carriers linked to one UL carrier.The seventh method has an advantage in that Tx overhead of UL grantinformation is distributed according to respective DL carriers.

8) Eighth method: According to the eighth method, a DCI format for ULgrant information may have the same length as other DCI formats as inthe DL scheduling assignment. As a result, although UL grant informationis transmitted through several DL component carriers linked to one ULcomponent carrier, UE blind decoding complexity is not increased. Thatis, assuming that the same information bit size is assigned not only toa bandwidth of a specific DL control information format instead of ULgrant information, but also to all bandwidths of a DL controlinformation format of the UL grant information, the UE can perform ratematching and CRC only in a region belonging to the correspondinginformation bit in association with two formats. That is, except for theblind decoding complexity for a control channel element (CCE)aggregation level, the blind decoding complexity caused by rate matchingis not increased. According to the above-mentioned 8^(th) method, it ispreferable that a specific DL control information format that has thesame length as that of a DL control information format of the UL grantinformation may use a different ID than a UE cell ID (i.e., C-RNTI) usedfor decoding UL grant information.

9) 9^(th) method: Carriers for receiving a PDCCH recognized by the LTE-AUE may be restricted to carriers incapable of being accessed by the LTEUE. As a result, control channel complexity caused by schedulinginformation transmission at each DL carrier may be distributed accordingto individual carriers.

Next, a method for effectively transmitting a PDCCH during the crosscarrier scheduling according to another embodiment of the presentinvention will hereinafter be described in detail.

If the cross carrier scheduling is allowed and the UE decodes a PDCCHfor all the DL component carriers, the blind decoding overhead isunavoidably increased. Therefore, the DL component carrier transmittinga PDCCH is restricted as in the above-mentioned UL grant transmissionmethod (i.e., 6^(th) method), such that blind decoding complexity andefficiency of carrier indicator (CI) information can be guaranteed.There are three methods 1) to 3) for selecting/establishing a DLcomponent carrier to transmit a PDCCH during cross carrier schedulingaccording to the present invention, and a detailed description thereofis as follows: 1) First Method: An LTE BC component carrier satisfyingthe default Tx-Rx separation condition may be selected as a DL componentcarrier for PDCCH transmission. 2) Second Method: Cell-specific,UE-specific, or UE group-specific primary carrier maybe selected as a DLcomponent carrier for PDCCH transmission. 3) Third Method: A DLcomponent carrier corresponding to a PDCCH monitoring set explicitlytransmitted through separate signaling may be selected as a DL componentcarrier for PDCCH transmission.

The above-mentioned three methods 1) to 3) are optional, and each methodmaybe independently used or two or more methods may be simultaneouslyassociated and used.

Detailed operations of a UE according to the above-mentioned methods 1)to 3) will be given below.

A PDCCH monitoring set may be semi-statically established through adedicated signaling method such as a UE-specific RRC signaling, and maybe transmitted as in UE DL CC set information and UE UL CC setinformation. In addition, when the BS transmits UE-specific carrierallocation information (e.g., UE DL CC set, UE UL CC set, and PDCCHmonitoring set) to the UE through dedicated signaling, the BS may informthe UE whether the cross carrier scheduling is enabled (activated).

If the cross carrier scheduling is enabled (activated) when the UEreceives UE-specific carrier setup information, the blind decoding maybe performed on a downlink control information format including acarrier indicator (CI) field. In contrast, if the cross carrierscheduling is deactivated, the blind decoding may be performed on adownlink control information format not including the CI field.

Besides the explicit cross carrier scheduling activation/deactivation,as an example of a method for enabling the UE to implicitly decidewhether the cross carrier scheduling is performed, the UE according tothe present invention can determine whether cross carrier scheduling isperformed on the basis of the presence or absence of the PDCCHmonitoring set information. That is, if information regarding the PDCCHmonitoring set is transmitted simultaneously with the UE-specificcarrier assignment information that is transmitted through dedicatedsignaling, the UE has only to decode a PDCCH within the correspondingset. Therefore, the UE determines that cross carrier scheduling has beenactivated, such that it may perform the blind decoding of a DL controlinformation format including a carrier indicator (CI) field.

In contrast, when the UE-specific carrier setup information istransmitted through dedicated signaling, if information regarding thePDCCH monitoring set is not contained in the UE-specific carrier setupinformation, a UE DL CC set may be used as DL CCs, each of which is usedas a reception target of PDSCH/PDCCH. Thus, the UE decides that thecross carrier scheduling has been deactivated, such that the UE mayperform the blind decoding of a downl ink control information format notincluding the carrier indicator (CI) field.

In accordance with another exemplary method of the present invention,when the BS transmits information of the PDCCH monitoring set to theLTE-A UEs, information regarding monitoring component carriers for theDL grant and information regarding monitoring component carriers for theUL grant are transmitted in different ways. That is, each componentcarrier to which the DL grant is transmitted is distinguished from eachcomponent carrier to which the UL grant is transmitted, such that the UEmay receive only the DL grant at a specific DL component carrier and mayalso receive only the UL grant at another DL component carrier.

UL Grant

A method for effectively transmitting and receiving a UL grant in amulti-carrier environment according to still another embodiment of thepresent invention will hereinafter be described in detail.

Under the condition that DCI format 0 specified in the LTE Rel.8 is usedas a format of the UL grant, if the number of UL component carriersavailable to an arbitrary UE is higher than the number of DL componentcarriers, the corresponding UE is unable to recognize which UL componentcarrier is used for PUSCH resource assignment information afterreceiving the UL grant received through the DL component carrier.Therefore, in order to support asymmetric carrier aggregation, there isneeded a method for informing the UL grant of information as to which ULcomponent carrier is used for PUSCH resource assignment information uponreceiving the corresponding UL grant.

For this purpose, the embodiment of the present invention provides thefollowing methods.

In a first method, the UL grant may explicitly include a carrier indexthat indicates which UL component carrier resource is indicated by thecorresponding UL grant.

In another method, n UL component carriers linked to a DL componentcarrier having received the UL grant are sequentially arranged accordingto a predetermined reference, and index information indicating which ULcomponent carrier receives the UL grant may be transmitted to the UE.For example, if 5 UL component carriers are linked to one DL componentcarrier, index information may have a size of 3 bits.

In still another method, the DCI format of the UL grant may be used as afixed DCI format according to either the number of available (candidate)UL component carriers of the UE or the number of active UL componentcarriers of the UE. In this case, the available (candidate) UL componentcarriers of the UE or the active UL component carriers may be notifiedto the UE through upper layer signaling, or may be UL component carriersoverridden through L1/L2 signaling (overridden UL component carriers areencountered when a carrier setup of the cell is ignored) from amongcomponent carriers well known to the UE through upper layer signaling.In this case, the UE may perform blind decoding of a DCI format of theUL grant according to either the number of available (candidate) ULcomponent carriers or the number of active UL component carriers. Thus,although the number of candidate UL component carriers or the number ofactive UL component carriers is not identical to the number of ULcomponent carriers actually scheduled in the corresponding subframe, theUE can recognize the number of UL component carriers and informationregarding the scheduling or non-scheduling of each UL component carrierthrough information regarding the corresponding DCI format.

In the above-mentioned UL/DL grant information, the number of bits of acarrier indicator (CI) is determined according to the number ofavailable UL/DL carriers assigned from the BS to the UE, and may beirrelevant to the number of actually used carriers as necessary. Inother words, although the BS may be operated using a smaller number ofcarriers from among a predetermined number of carriers assigned to theBS at a specific time, it is undesirable that the number of bits of thecarrier indicator (CI) contained in the grant information is changed inso far as the BS does not change the number of available carriers.

Physical Hybrid ARQ Indicator Channel (PHICH)

A method for effectively transmitting and receiving a PDCCH in amulti-carrier environment according to still another embodiment of thepresent invention will hereinafter be described in detail.

Although this embodiment assumes a DL heavy status in which two DLcarriers are linked to one UL carrier as shown in FIG. 9( a) forconvenience of description and better understanding of the presentinvention, it should be noted that this embodiment of the presentinvention can also be applied to multi-carrier aggregation of thesymmetrical- and UL heavy-types without departing from the scope andspirit of the present invention.

In accordance with this embodiment, the following two methods may beused to transmit a PHICH acting as feedback information (HARQ ACK/NACK)that indicates whether a reception error of a PUSCH transmitted throughone UL component carrier occurs.

In accordance with the first method, a PHICH is transmitted through allDL component carriers linked to one UL component carrier. In accordancewith the second method, a PHICH is transmitted through only one ofseveral DL component carriers linked to one UL component carrier.

The first method is based on the aspect that resources for a PHICH arepre-reserved at a DL carrier for use in the LTE Rel.8 system. If PHICHresources are assigned at each layer, it is not necessary to assign aPHICH through only one carrier without using the pre-assigned resources.

If the first method is applied, the same PHICH for one PUSCH istransmitted to a plurality of DL component carriers, so that the UE canreceive the PHICH through several carriers, resulting in increasedreception reliability.

For PHICH assignment, an uplink lowest resource block index (UL lowestRB index) used for the corresponding PUSCH resource assignment and ademodulation reference signal cyclic shift (DM RS CS) on the UL grantare used. In this case, if several PHICHs are transmitted throughmultiple carriers, a number of the used PHICH group and a PHICHorthogonal sequence index (OS index) may be identical to each other, ormay be differently assigned using a different parameter such as acarrier index.

Alternatively, in order to differently assign the PHICH group number andthe PHICH orthogonal sequence index during the assignment of severalPHICHs, the BS may transmit the UL grant for one PUSCH through severalcarriers. However, under the condition that the same resource assignmentinformation is assigned to several UL grant messages for one PUSCH, theBS may assign different DM RS CS values to respective UL grant messages,or may also use such several UL grant information to assign a PHICH.

The second method can be more effectively used when the BS supports acarrier to which a PDCCH or PHICH is not transmitted. For this purpose,the present invention provides a variety of methods 1) to 10) forselecting any one DL component carrier to be used for PHICH transmissionfrom among several DL component carriers linked to one UL componentcarrier, and a detailed description thereof will be given below. Acarrier to which a PHICH is to be transmitted through the followingmethods may be selected as a UE-specific carrier or a cell-specificcarrier.

1) First Method: If a primary carrier from among DL component carrierslinked to one UL component carrier is established according to apredetermined reference, a PHICH may be transmitted through acorresponding DL primary carrier. In this case, the primary carrier maybe cell-specific or UE-specific. In this case, the primary carrier maybe established per DL/UL linkage irrespective of DL/UL.

2) Second method: When deciding the order of DL component carrierslinked to one UL carrier, a PHICH may be transmitted through the firstor last carrier on the basis of a DL EARFCN.

3) Third Method: In association with DL component carriers linked to oneUL component carrier, a DL component carrier to which one PHICH is to betransmitted may be determined using the pre-defined rule such as ahashing function known to both the BS and the UE. In this case, the DLcomponent carrier may have cell-specific, UE-specific, or UEgroup-specific characteristics.

4) Fourth Method: In accordance with the fourth method, a PHICH may betransmitted through a DL component carrier to which a UL grant for thecorresponding

PUSCH expecting to receive the PHICH is transmitted. The fourth methodmay correspond to a case in which the above-mentioned methods proposedby the present invention are used. Even when the BS transmits the ULgrant through downlink carriers linked to one UL component carrier inthe same manner as in the above-mentioned method, the fourth method mayalso be used. A detailed description of the fourth method will bedescribed later.

5) Fifth Method: The fifth method can determine a DL component carrierthat can be used to automatically transmit a PHICH by a UE ID assignedto each UE, from among DL carriers linked to one UL carrier. Forexample, provided that the number of DL component carriers linked to oneUL component carrier is denoted by ‘n’, a DL component carrier to whicha PHICH is to be transmitted may be determined by applying a modulooperation based on the ‘n’ value to the UE ID value, such that a DLcomponent carrier to which a PHICH is to be transmitted can bedetermined.

The above-mentioned method has an advantage in that Tx overhead of aPHICH is distributed to respective DL carriers.

6) Sixth Method: In accordance with the sixth method, the BS selects aDL component carrier to which the UL grant is to be transmitted usingthe above-mentioned fifth method, so that the UL grant is transmitted tothe UE. Thereafter, a PHICH associated with a PUSCH that has beentransmitted using the corresponding UL grant may be transmitted througha DL component carrier to which the corresponding UL grant has beentransmitted as in the above-mentioned fourth method.

7) Seventh Method: If the number of DL carriers capable of beingaccessed by the LTE-based UE from among several DL component carrierslinked to one UL carrier is limited to a predetermined number (<thetotal number of DL component carriers), a PHICH may be set to any DLcomponent carrier that can be accessed by the LTE-based UE, such that acommon design (i.e. downward compatibility) for the LTE standard can beguaranteed. In contrast, in order to achieve PDCCH load balancing, aPHICH for the LTE-A UE may be transmitted through a DL component carrierthat can be accessed only by the LTE-A UE.

8) Eighth Method: Assuming that a specific DL component carrier canaccess the LTE-based UE using the above-mentioned seventh method, thismeans that the corresponding carrier satisfies the FDD default Tx-Rxseparation condition defined in the LTE Rel-8. Therefore, assuming thatthe ratio of DL to UL carriers is set to 2:1, only one DL/UL pair cansatisfy the above-mentioned default Tx-Rx separation condition.

For the above-mentioned reason, according to the 8^(th) method, only oneof two DL component carriers can be accessed by the LTE-based UE, suchthat a PHICH can be transmitted through the accessed DL componentcarrier only.

9) Ninth Method: If the BS supports a carrier to which a PDCCH or PHICHis not transmitted from among multiple carriers, a PHICH may betransmitted only through a DL component carrier in which PDCCH or PHICHtransmission is not limited.

In accordance with the ninth method, physical resource mapping of aPHICH may be affected by a PHICH duration transmitted over a PBCH. Inaddition, a PHICH duration and a PCFICH are correlated with each otherto occupy a control channel region, and are configured to greatly affectPHICH resource region assignment. The PHICH duration transmitted througha PBCH is indicated by one bit, and each of a normal duration and anextended duration of the PHICH duration is indicated by one bit. If thePHICH duration is a normal duration, the number of OFDM symbols used forPHICH assignment is always set to 1, and the number of OFDM symbols,each of which receives a PDCCH, may be determined according to a controlchannel format indicator (CFI) value of a PCFICH at a DL componentcarrier independently from one OFDM symbol used for PHICH assignment. Ifthe PHICH duration is an extended duration, the number of OFDM symbolsused for PHICH assignment is always set to 3. In this case (i.e., in thecase where FDD is performed and an MBSFN subframe is not present), thecontrol channel format indicator (CFI) value of a PCFICH should alwaysbe set to 3.

Therefore, in order to support a carrier to which a PDCCH or PHICH isnot transmitted, the UE may ignore a PHICH duration transmitted over aprimary broadcast channel (PBCH) on the basis of correlation between aPBCH and a PCFICH, and may not expect to receive a PHICH at a specificcarrier. In accordance with a method for transmitting a PCFICH proposedin one embodiment of the present invention, in order to indicatenon-assignment of a PDCCH, a reserved bit value (0b11) of the controlchannel format indicator (CFI) maybe used, or a conventional 2-bitcontrol channel format indicator (CFI) may be differently interpreted as{0, 1, 2, 3}.

That is, the BS includes PHICH duration information in a PBCHtransmitted through multiple aggregated DL component carriers. Inaddition, the BS carrier-specifically transmits a PCFICH and the controlchannel format indicator (CFI) indicates the number {0, 1, 2, or 3} ofOFDM symbols used for PDCCH transmission. In the case where the controlchannel format indicator (CFI) value contained in the PCFICH at anarbitrary DL component carrier is set to zero OFDM symbol, the UE mayoverride information of the PHICH duration transmitted to the PBCH andmay not expect to receive a PDCCH and a PHICH at the correspondingcarrier.

Namely, from the viewpoint of UE operations, if a control channel formatindicator (CFI) value of a PCFICH transmitted through a DL componentcarrier denotes ‘0’ so that a control channel region is not allocated tothe corresponding carrier, the UE may override information of the PHICHduration received over a PBCH and PHICH resource assignment information,may perform blind decoding of a control channel at the correspondingcarrier or may not receive a PHICH at the corresponding carrier, suchthat downlink resources can be effectively utilized using theabove-mentioned method.

10) Tenth Method: The tenth method includes an index of a DL carrier tobe used for PHICH reception in PDCCH. While the above-mentioned methodsselect a DL carrier to be used for PHICH reception according to theregular rules, if a DL carrier indicator for a PHICH is contained in thePDCCH, the BS can freely select a DL carrier and transmit the UL grantinformation. In this case, PHICH collision or PHICH distribution for aMulti-User MIMO (MU-MIMO) can be freely performed.

A method for effectively transmitting and receiving a PHICH in a crosscarrier scheduling situation according to another aspect of the presentinvention will hereinafter be described in detail.

FIG. 10 shows a PHICH transmission format in a cross-carrier schedulingsituation according to another embodiment of the present invention.

In FIG. 10, it is assumed that the BS allows the cross carrierscheduling and two DL component carriers are linked to two UL componentcarriers one by one (1:1).

In this case, the cross carrier scheduling for UL grant information isapplied, so that UL grant information for a PUSCH to be transmitted to aUL component carrier #2 may be transmitted to a DL component carrier #1.In this case, this embodiment of the present invention provides thefollowing two methods to determine a DL component carrier at which aPHICH carrying feedback information (ACK/NACK) for a PUSCH transmittedthrough a UL component carrier #2 is received.

1) First Method: In accordance with the first method, a DL componentcarrier to which UL grant information indicating the corresponding PUSCHis transmitted is determined to be a DL component carrier at which aPHICH for the corresponding UL grant is to be received.

2) Second Method: In accordance with the second method, a DL componentcarrier linked to a UL component carrier of a PUSCH indicated by ULgrant information is determined to be a DL component carrier at which aPHICH for the corresponding UL grant information is to be received.

The first and second methods are classified according to three cases byreferring to FIG. 10, and a detailed description thereof will be givenbelow.

First, in a first case (a) shown in FIG. 10, the UL grant #1 for a PUSCH#1 is transmitted from a control region of the DL component carrier #1(1001), and a PUSCH #1 indicated by the UL grant #1 is transmittedthrough a UL component carrier #1 (1002). In the first case (a), thecross carrier scheduling is not performed, so that the carrier indicator(CI) field may not be contained in the corresponding PDCCH.

PHICH #1 indicating feedback information (ACK/NACK) for the PUSCH #1 maybe transmitted through a DL component carrier #1 (1003). In this case,the above-mentioned two methods may provide the same results. That is,the DL component carrier #1 is always used for PHICH transmission.

Next, in a second case (b) shown in FIG. 10, the UL grant #2 for a PUSCH#2 is transmitted from a control region of the DL component carrier #1(1001), and a PUSCH #2 indicated by the UL grant #2 is transmittedthrough a UL component carrier #2 (1012). In the second case (a), thecross carrier scheduling is performed, so that the carrier indicator(CI) field indicating the UL component carrier #2 may be contained inthe corresponding PDCCH.

PHICH #2 indicating feedback information (ACK/NACK) for the PUSCH #2 maybe transmitted through a DL component carrier #1 (1003). This means thata PHICH is operated according to the above-mentioned first method (a).As a result, in the cross carrier scheduling situation, the UE need notmonitor a control region of all DL component carriers, resulting in areduction in the UE blind decoding overhead.

Next, in a third case (c) shown in FIG. 10, a UL grant #2 for a PUSCH #2is transmitted from a control region of a DL component carrier #1(1001), and a PUSCH #2 indicated by the UL grant #2 is transmittedthrough a UL component carrier #2 (1012). In the third case (c), thecross carrier scheduling is performed, so that the carrier indicator(CI) field indicating the UL component carrier #2 may be contained in aPDCCH.

PHICH #2 indicating feedback information (ACK/NACK) for a PUSCH #2 maybe transmitted through a DL component carrier #2 (1013). This case meansthat a PHICH is operated according to the above-mentioned second method(b).

UL ACK/NACK

A method for effectively transmitting and receiving a UL ACK/NACK in amulti-carrier environment according to another embodiment of the presentinvention will hereinafter be described in detail.

In a carrier aggregation situation, according to a linkage formatbetween DL and UL component carriers established in an upper layer, n DLcomponent carriers may be linked to an arbitrary UL component carrier.In this case, after a Cyclic Redundancy Check (CRC) is attached toPDSCHs through respective DL component carriers, additional channelcoding is performed on the PDSCHs, so that the resultant PDSCHs can besimultaneously transmitted. In this case, there are a variety of methodsto transmit a UL feedback (UL ACK/NACK) according to another embodimentof the present invention, and a detailed description thereof will begiven below.

1) First method: In a first method, as to N feedback information(NACK/NACK information) for N PDSCH transmission times throughrespective DL component carriers, the UE performs ACK/NACK bundlingthrough only one value and transmits information of the bundling resultto the BS. In this case, PUCCH resource assignment for the bundledACK/NACK information may be achieved based on a PDCCH lowest controlchannel element (CCE) index of a PDSCH transmitted via a primarycarrier. Alternatively, PUCCH resource assignment may be achieved basedon a modulo operation related to the number of DL component carriers,each of which receives a PDSCH for a UE ID, or may be achieved based ona PDCCH lowest CCE index for a PDSCH of DL component carriers to whichthe corresponding PDSCH is transmitted (i.e., a DL component carrierwith the lowest index, a DL component carrier with the highest index,and a DL component carrier with an arbitrary fixed index).

2) Second Method: In accordance with a second method to transmit ULACK/NACK information, PUCCH resources {2D sequence combination index ofZC sequence cyclic shifting (CS) Walsh cover, and a slot-directionalpair index (herein, setting of mix resource block is possible) of afrequency domain physical resource block (PRB)} are identified anddifferently assigned on a UL component carrier linked to respective DLcomponent carriers to which PDSCHs are simultaneously transmitted. As aresult, UL ACK/NACK PUCCH resources may be assigned on the basis of aPDCCH lowest CCE index for the corresponding PDSCH of each DL componentcarrier in the corresponding PUCCH resource region.

3) Third Method: Each PDCCH lowest CCE index of respective DL componentcarriers to which PDSCHs are simultaneously transmitted is replaced witha virtual CCE index, and UL ACK/NACK information corresponding to thereplaced index is assigned to a PUCCH. In more detail, CCE indexsequences of individual DL component carriers linked to an arbitrary ULcomponent carrier are arranged in the order of carrier indexes of thecorresponding DL component carriers to which a PDSCh is transmitted,such that a logical virtual CCE index sequence may be constructed. Basedon the aforementioned index sequence, if a PDSCH is transmittedaccording to individual DL component carriers, a lowest CCE index of aPDCCH correspondent to the PDSCH is replaced with a virtual CCE indexvalue in such a manner that the PDCCH lowest CCE index may be mapped tothe logical virtual CCE index sequence. Thus, the mapped virtual CCEindex sequence may be applied to PUCCH allocation of the correspondentUL ACK/NACK information.

A method for effectively transmitting and receiving UL ACK/NACKinformation serving as UL feedback in a cross carrier schedulingsituation according to another embodiment of the present invention.

In a UL heavy status in which the number of UL component carriers ishigher than the number of DL component carriers as shown in FIG. 9( b),during transmission of UL ACK/NACK in response to DL data transmission,the problems encountered in UL grant transmission and PHICH transmissionmay occur as in the above-mentioned embodiments. That is, UL ACK/NACKfor one DL data transmission may be transmitted via all of the pluralityof UL component carriers 1 inked to one DL component carrier, or mayalso be transmitted via only some of the plurality of UL componentcarriers.

If the UL ACK/NACK information for one DL data transmission istransmitted through several UL component carriers, this means thatresources of several UL component carriers are used to transmit the sameinformation, resulting in ineffective utilization of UL resources.

In addition, when considering UE multiplexing in which the number ofallocated DL component carriers is higher than the number of ULcomponent carriers, namely, if UL ACK/NACK for several PDSCHs needs tobe transmitted through one UL carrier, it is preferable that UL ACK/NACKbe transmitted only through one or more UL component carriers.

Considering the above-mentioned reason, a variety of methods forselecting a UL component carrier to which UL ACK/NACK is to betransmitted from among UL component carriers linked to one DL componentcarrier according to still another embodiment of the present inventionwill hereinafter be described in detail. By the above-mentionedmethods 1) to 6), a UL component carrier to which UE-specific, UEgroup-specific, or cell-specific UL ACK/NACK is to be transmitted, maybe selected.

1) First Method: In a first method, if a primary carrier is selectedfrom among UL component carriers linked to one DL component carrieraccording to a predetermined reference, UL ACK/NACk information may betransmitted through the corresponding UL primary carrier. In this case,the primary carrier may be cell-specific or UE-specific as necessary.The primary carrier maybe established per DL/UL linkage, -irrespectiveof DL/UL.

2) Second Method: When deciding the order of UL component carrierslinked to one DL component carrier, UL ACK/NACK may be transmitted onlythrough the first or last carrier as necessary.

3) Third Method: In association with UL component carriers linked to oneDL component carrier, a UL component carrier to which one or more ULACK/NACK information for each linkage is to be transmitted may bedetermined using a predefined rule such as a hashing function known tothe UE and the BS. In this case, the UL component carrier may becell-specific, UE-specific, or UE group-specific.

4) Fourth Method: The fourth method can determine a UL componentcarrier, that can automatically transmit UL grant information by a UE IDassigned to each UE, from among UL carriers linked to one DL carrier.The fourth method has an advantage in that Tx overhead of UL ACK/NACKinformation is distributed according to respective UL carriers.

5) Fifth Method: Feedback information (ACK/NACK) of the corresponding DLdata is contained in a control channel (i.e., PDCCH) of DL data in sucha manner that a UL component carrier to be transmitted from the UE tothe BS can be explicitly indicated.

6) Sixth Method: Through a predetermined field from among a DCI formatof DL data transmitted via a PDCCH, a UL component carrier that is goingto implicitly transmit UL feedback information may be notified of theUE.

Apparatus-UE and BS

Now a description will be given of a UE and a BS for implementing theabove-described exemplary embodiments of the present invention,according to another exemplary embodiment of the present invention.

The UE may operate as a transmitter on an uplink and as a receiver on adownlink, while the BS may operate as a receiver on the uplink and as atransmitter on the downlink. That is, each of the UE and the BS mayinclude a transmitter and a receiver for transmission and reception ofinformation or data.

The transmitter and the receiver may include processors, modules, parts,and/or means for implementing the exemplary embodiments of the presentinvention. Especially, the transmitter and the receiver may include amodule (means) for encrypting messages, a module for interpretingencrypted messages, an antenna for transmitting and receiving messages,etc. An example of the transmitter and the receiver will be describedbelow with reference to FIG. 11.

FIG. 11 is a block diagram of a transmitter and a receiver according toanother exemplary embodiment of the present invention.

Referring to FIG. 11, the left part corresponds to the transmitter andthe right part corresponds to the receiver. Each of the transmitter andthe receiver may include an antenna 11055 or 1110, a processor 1120 or1130, a Transmission (Tx) module 1140 or 1150, a Reception (Rx) module1160 or 1170, and a memory 1180 or 1190. The components of thetransmitter are complementary to those of the receiver. The componentsof the transmitter and the receiver will be described below in moredetail.

The antennas 1105 and 1110 include Tx antennas for transmitting signalsgenerated from Tx modules 1140 and 1150 and Rx antennas for receivingradio frequency (RF) signals and providing the received RF signals tothe Rx modules 1160 and 1170. If Multiple Input Multiple Output (MIMO)is supported, two or more antennas may be provided.

The processors 1120 and 1130 generally provide overall control to theUE. Especially, the processors 1120 and 1130 may perform a controllerfunction for implementing the above⁻described exemplary embodiments ofthe present invention, a variable Medium Access Control (MAC) framecontrol function based on service characteristics and a propagationenvironment, a handover (HO) function, an authentication and encryptionfunction, etc.

Especially, the processor of the UE controls overall UE operationsrequired for transmitting/receiving physical channels in a multi-carrierenvironment, such that the UE can transmit and receive data to and froma base station (BS) or a relay station.

For example, the processor may determine the number of UL componentcarriers, the number of DL component carriers, and a linkage between ULand DL component carriers, according to carrier setup informationallocated from the BS or the relay station.

Thereafter, the processor can receive the UL grant information from theBS through any DL component carrier from among several DL componentcarriers available to the processor, and can transmit a PUSCH to the BSthrough UL resources indicated by the UL grant. In this case, ULresources indicated by the UL grant may be a carrier linked to a DLcomponent carrier where the UL grant has been received, or may be adifferent UL component carrier not linked to the DL component carrier.In the latter case, cross carrier scheduling is achieved. The processorcontrols the Rx module, such that it can receive feedback information(ACK/NACK) indicating whether there arises a reception error of a PUSCHthat has been transmitted through a PHICH belonging to the same DLcomponent carrier as a DL component carrier that has received the ULgrant from the BS after the lapse of a predetermined number of frames.

The above-mentioned processor operation can be applied to both a DLheavy status and a UL heavy status depending on numbers of DL and ULcomponent carriers available to the UE.

Besides, detailed functions for transmitting/receiving various physicalchannels on other data transmission process are identical to those ofthe above-mentioned embodiments of the present invention, and as such adetailed description thereof will herein be omitted for convenience ofdescription.

The Tx modules 1140 and 1150 may encode and modulate transmission datascheduled by the processors 1120 and 1130 according to a predeterminedcoding and modulation scheme and provide the modulated data to theantenna 1110.

The Rx modules 1160 and 1170 may recover original data by demodulatingand decoding data received through the antennas 1105 and 1110 andprovide the recovered data to the processors 1120 and 1130.

The memories 1180 and 1190 may store programs for processing and controlof the processors 1120 and 1130 and temporarily store input/output (I/O)data. Each of the memories 1180 and 1190 may include at least one typeof storage media such as a flash memory, a hard disk, a multimedia cardmicro, a card-type memory (e.g. a Secure Digital (SD) or eXtreme Digital(XD) memory), a Random Access Memory (RAM), a Static Random AccessMemory (SRAM), a Read-Only Memory (ROM), an Electrically ErasableProgrammable Read-Only Memory (EEPROM), a Programmable Read-Only Memory,a magnetic memory, a magnetic disc, an optical disc, etc.

In the meantime, the BS may perform a control function for implementingthe above-described exemplary embodiments of the present invention,Orthogonal Frequency Division Multiple Access (OFDMA) packet scheduling,Time Division Duplex (TDD) packet scheduling and channelization, avariable MAC frame control function based on service characteristics anda propagation environment, a real-time high-speed traffic controlfunction, a handover function, an authentication and encryptionfunction, a packet modulation/demodulation function for datatransmission and reception, a high-speed packet channel coding function,a real-time MODEM control function, etc., by at least one of theabove-described modules, or the BS may further include an additionalmodule, part or means for performing these functions.

Those skilled in the art will appreciate that the present invention maybe carried out in other specific ways than those set forth hereinwithout departing from the spirit and essential characteristics of thepresent invention. The above exemplary embodiments are therefore to beconstrued in all aspects as illustrative and not restrictive. The scopeof the invention should be determined by the appended claims and theirlegal equivalents, not by the above description, and all changes comingwithin the meaning and equivalency range of the appended claims areintended to be embraced therein. Also, it will be obvious to thoseskilled in the art that claims that are not explicitly cited in theappended claims may be presented in combination as an exemplaryembodiment of the present invention or included as a new claim bysubsequent amendment after the application is filed.

INDUSTRIAL APPLICABILITY

The embodiments of the present invent ion have exemplarily disclosed notonly a method for effectively transmitting/receiving a physical channelin a multi-band environment, but also a UE structure therefor, and themethod and UE structure thereof have been exemplarily applied to the3GPP LTE system for convenience of description. Of course, theembodiments of the present invention may also be applied not only to the3GPP LTE system but also to other mobile communication systems each ofwhich has a multi-band environment without departing from the scope orspirit of the present invention.

1.-13. (canceled)
 14. A method for transmitting data carried out by auser equipment (UE) in a wireless access system supportingmulti-carriers, the method comprising: receiving a first uplink (UL)grant information for a first UL component carrier (CC) from a basestation (BS) through a first control channel of a first downlink (DL) CCamong a plurality of DL CCs available for the UE; transmitting data tothe BS through uplink (UL) resources indicated by the first UL grantinformation; and receiving feedback infoiiiiation indicating a receptionstatus of the transmitted data from the base station through a secondcontrol channel of the first DL CC.
 15. The method according to claim14, wherein the first UL CC is linked with a plurality of DL CCsincluding the first DL CC.
 16. The method according to claim 14, whereinthe reception of the feedback information is performed at a subframewhich comes after a predetermined number of subframes from a subframeindicated by the first UL grant information.
 17. The method according toclaim 14, wherein the first control channel is a Physical DownlinkControl Channel (PDCCH) and the second channel is a Physical Hybrid ARQIndicator Channel (PHICH).
 18. A method for receiving data carried outby a base station (BS) in a wireless access system supportingmulti-carriers, the method comprising: transmitting a first uplink (UL)grant information for a first UL component carrier (CC) to a userequipment (UE) through a first control channel of a first downlink (DL)CC among a plurality of DL CCs available for the UE; receiving data fromthe UE through uplink (UL) resources indicated by the first UL grantinformation; determining a reception status of the received data; andtransmitting feedback information indicating the determined receptionstatus to the UE through a second control channel of the first DL CC.19. The method according to claim 18, wherein the feedback informationis transmitted through the first DL CC only.
 20. The method according toclaim 18, wherein the uplink (UL) resources are uplink resources of anuplink (UL) component carrier not linked to the first DL componentcarrier.
 21. The method according to claim 18, wherein the first UL CCis linked with a plurality of DL CCs including the first DL CC.
 22. Themethod according to claim 18, wherein the transmission of the feedbackinformation is performed irrespective of a ratio between the number ofDL CCs available in the user equipment (UE) and the number of UL CCsavailable in the user equipment (UE).
 23. The method according to claim18, wherein the first control channel is a Physical Downlink ControlChannel (PDCCH) and the second channel is a Physical Hybrid ARQIndicator Channel (PHICH).
 24. The method according to claim 18, whereinthe reception of the feedback information is performed at a subframewhich comes after a predetermined number of subframes from a subframeindicated by the first UL grant information.
 25. A user equipment (UE)operated in a wireless access system supporting multi-carriers, the UEcomprising: a processor; and a radio frequency (RF) module fortransceiving a radio frequency (RF) signal externally under a control ofthe processor, wherein the processor, upon receiving a first uplink (UL)grant infoiniation for a first UL component carrier (CC) from a basestation (BS) through a first control channel of a first downlink (DL) CCamong a plurality of DL CCs available for the UE, transmits data to theBS through uplink (UL) resources indicated by the first UL grantinformation, receives feedback infoimation indicating a reception statusof the transmitted data from the base station through a second controlchannel of the first DL CC.
 26. The user equipment (UE) according toclaim 25, wherein the first UL CC is not linked to the first DL CC. 27.The user equipment (UE) according to claim 25, wherein the processor isconfigured to receive the feedback information through the secondcontrol channel of the first DL CC, irrespective of a ratio between thenumber of DL CCs available in the user equipment (UE) and the number ofUL CCs available in the user equipment (UE).
 28. The user equipment (UE)according to claim 25, wherein the first UL CC is linked with aplurality of DL CCs including the first DL CC.
 29. The user equipment(UE) according to claim 25, The user equipment (UE) according to claim11, wherein the processor is configured to receive the feedbackinformation at a subframe which comes after a predetermined number ofsubframes from a subframe indicated by the first UL grant information.30. The user equipment (UE) according to claim 25, wherein the firstcontrol channel is a Physical Downlink Control Channel (PDCCH) and thesecond channel is a Physical Hybrid ARQ Indicator Channel (PHICH).